The present invention relates to a gas turbine split ring and. More specifically, this invention relates to a split ring which appropriately secures an interval (chip clearance) with respect to a tip end of a moving blade in the operating state of a gas turbine (under high temperatures).
FIG. 10 shows a general section view showing a front stage part in a gas passage part of a gas turbine. In the drawing, to an attachment flange 31 of a combustor 30, an outer shroud 33 and an inner shroud 34 which fix each end of a first stage stationary blade (1c) 32 are attached, and the first stage stationary blade 32 is circumferentially arranged in plural about the axis of the turbine and fixed to the cabin on the stationary side.
On the downstream side of the first stage stationary blade 32, a first stage moving blade (1s) 35 is arranged in plural, and the first stage moving blade 35 is fixed to a platform 36, the platform 36 being fixed to the periphery of a rotor disc so that the first stage moving blade 35 rotates together with the rotor. Furthermore, in the periphery to which the tip end of the first stage moving blade 35 neighbors, a split ring 42 of circular ring shape having a plural split number is attached and fixed to the side cabin side.
On the downstream side of the first stage moving blade 35, a second stage stationary blade (2c) 37 of which each side is fixed to an outer shroud 38 and an inner shroud 39 is circumferentially attached in plural to the stationary side in the same manner as the first stage stationary blade 32. Furthermore, on the downstream side of the second stationary stage 37, a second stage moving blade (2s) 40 is attached to the rotor disc via a platform 41, and in the periphery to which the tip end of the second stage moving blade 40 neighbors, a split ring 43 of circular ring shape having a plural split number is attached.
The gas turbine having such a blade arrangement is configured by, for example, four stages, wherein high temperature gas 50 obtained by combustion in the combustor 30 enters from the first stage stationary blade 32, expands while flowing between each blade of the second to fourth stages, supplies rotation power to the rotor by rotating each of the moving blades 35, 40 or the like, and then is discharged outside.
FIG. 11 is a detailed section view of the split ring 42 to which the tip end of the first stage moving blade 35 neighbors. In this drawing, a number of cooling ports 61 are provided in an impingement plate 60 so as to penetrate through it, and this impingement plate 60 is attached to a heat shielding ring 65.
Also the split ring 42 is attached to the heat shielding ring 65 by means of cabin attachment flanges formed on both the upstream and downstream sides of main flow gas 80 which is the high temperature gas 50. Inside the split ring 42, a plurality of cooling passages 64 thorough which the cooling air passes are pierced in the flow direction of the main flow gas 80, and one opening 63 of the cooling passage 64 opens to the outer peripheral surface on the upstream side of the split ring 42, while another opening opens to the end surface on the downstream side.
In the above-mentioned configuration, cooling air 70 extracted from a compressor or supplied from an external cooling air supply source flows into a cavity 62 via the cooling port 61 of the impingement plate 60, and the cooling air 70 having flown into the cavity 62 comes into collision with the split ring 42 to forcefully cool the split ring 42, and then the cooling air 70 flows into the cooling passage 64 via the opening 63 of the cavity 62 to further cool the split ring 42 from inside, and is finally discharged into the main flow gas 80 via the opening of the downstream side.
FIG. 12 is a perspective view of the above-described split ring 42. As shown in the drawing, the split ring 42 is composed of a plurality of split structure segments divided in the circumferential direction about the axis of the turbine, and a plurality of these split structure segments are connected in the circumferential direction to form the split ring 42 having a circular ring shape as a whole. On the outside (upper side in the drawing) of the split ring 42 is provided the impingement plate 60 which forms the cavity 62 together with the recess portion of the split ring 42.
The impingement plate 60 is formed with a number of cooling ports 61, and the cooling air 70 flows into the cavity 62 via the cooling ports 61, comes into collision with the outer peripheral surface of the split ring 42, cools the split ring 42 from outer peripheral surface, flows into the cooling passage 64 via the opening 63, flows through the cooling passage 64, and is discharged into the main flow gas 80 from the end surface, whereby the cooling air 70 cools the split ring from inside in the course of passing through the cooling passage 64.
As described above, the split ring of the gas turbine is cooled by the cooling air, however, in the operating state of the gas turbine, since the surface of the split ring is exposed to the main flow gas 80 of extremely high temperature, the split ring will heat expand in both the circumferential and the axial direction.
The interval between the tip end of the moving blade of the gas turbine and the inner peripheral surface of the split ring becomes small under high temperatures or under the operating state due to the influence of centrifugal force and heat expansion in comparison with the situation under low temperatures or under the unoperating state, and it is usual to determine a design value and a management value of the tip clearance in consideration of the amount of change of this interval. In practice, however, the inner peripheral surface of the split ring often deforms into a shape which is not a shape that forms apart of the cylindrical surface because of a temperature difference between the inner peripheral side and the outer peripheral side of the split ring, so that there is a possibility that the rotating moving blade and the split ring at rest interfere with each other to cause damages of both members.
In view of the above situation, the applicant of the present invention has proposed a split ring in which for the purpose of suppressing the heat deformation under high temperatures, on the outer peripheral surface between two cabin attachment flanges in the split structure segments constituting the split ring, a circumferential rib extending in the circumferential direction and an axial rib extending in the direction parallel to the axis of the circular ring shape are formed in plural lines to provide a rib in the shape of a waffle grid as a whole (Japanese Patent Application No. 2000-62492). According to this invention, the rib in the form of a waffle grid suppresses the heat deformation, making it possible to secure an appropriate tip clearance.
However, even by the above proposition of the present applicant, that is, by formation of the rib in the form of a waffle grid, it is impossible to suppress the heat deformation of the split ring satisfactorily.
It is an object of the invention to provide a split ring which makes it possible to secure a tip clearance with respect to a tip end of a moving blade in the operating state of a gas turbine (under high temperatures).
The gas turbine split ring according to one aspect of the present invention is a gas turbine split ring which is provided on a peripheral surface in a cabin at a predetermined distance with respect to a tip end of a moving blade, the split ring being made up of a plurality of split structure segments that are connected in the circumferential direction to form the split ring of a circular ring shape, each split structure segment having cabin attachment flanges extending in the circumferential direction on both of the upstream and downstream sides of high temperature gas. On an outer peripheral surface between two cabin attachment flanges of the split structure segment, a circumferential rib which extends in the circumferential direction and an axial rib which extends in the direction parallel to the axis of the circular ring shape and has a height taller than the circumferential rib are formed in plural lines. That is, in this gas turbine split ring, the axial rib is formed to be higher than the circumferential rib in the waffle grid rib formed on the outer peripheral surface of the gas turbine split ring.
The height of the axial rib is designed to be larger than that of the circumferential rib as described above on the basis of the findings by means of simulation made by the inventors of the present application that heat deformation in the axial direction contributes to reduction of the tip clearance more largely than heat deformation in the circumferential direction. Also from the view point of not preventing the cooling air supplied via the cooling ports of the impingement plate from flowing into the openings of the cooling passages formed on the outer peripheral surface of the split ring, the height of the circumferential rib is suppressed.
That is, the split ring is formed by connecting a plurality of split structure segments in the circumferential direction as described above, and since a clearance is formed at the connecting portion in expectation of heat expansion under high temperatures, heat deformation can be absorbed more or less at this clearance part, while on the other hand, as for the axial direction, since two cabin attachment flanges are attached to the cabin without leaving a clearance, heat deformation cannot be absorbed, and the peripheral wall part between two cabin attachment flanges protrudes to the moving blade side to reduce the tip clearance.
In view of the above, according to the gas turbine split ring of the present invention, by forming the axial rib to be higher than the circumferential rib in the waffle grid rib formed on the outer peripheral surface of the split ring, the section modulus in the axial direction is made smaller than that of the conventional case, and the amount of heat deformation in the axial direction which contributes to the change of the tip clearance more largely than heat deformation in the circumferential direction, with the result that it is possible to suppress the change of the tip clearance due to a temperature difference compared to the conventional case.
The gas turbine split ring according to an another aspect of the present invention is a gas turbine split ring which is provided on a peripheral surface in a cabin at a predetermined distance with respect to a tip end of a moving blade, the split ring being made up of a plurality of split structure segments that are connected in the circumferential direction to form the split ring of a circular ring shape, each split structure segment having cabin attachment flanges extending in the circumferential direction on both of the upstream and downstream sides of high temperature gas. The split ring is formed to have a shape before heat deformation such that the inner peripheral surface of the split structure segment and the tip end of the moving blade has a predetermined interval in heat deformed condition in the operating state of the gas turbine.
In the above-mentioned gas turbine split ring, the split ring is formed into a shape in expectation of heat deformation so that the tip clearance becomes a predetermined clearance in the condition after heat deformation regardless of presence/absence of the waffle grid rib.
According to the gas turbine split ring, the shape of the split ring before heat deformation is formed in expectation of heat deformation regardless of presence/absence of the waffle grid rib, with the result that it is possible to control the tip clearance after heat deformation more properly.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.